FR 2,910,047 describes an inflatable sleeve, also called packer by those skilled in the art, with a cylindrical sleeve made from elastomer covered with a textile containing sheath. The tubular sheath has a cylindrical shape at rest. It can be expanded to a maximum expansion state, where it adopts a predetermined profile from which it opposes a very high resistance to any additional expansion. The tubular sheath is made from a textile material, comprising elastic peripheral yarns and, secondarily, longitudinal yarns extending in a direction parallel to the axis of the sleeve. The control of the predetermined profile of the sheath is provided by the peripheral yarns. The elongation capacity and ultimate strength of these peripheral yarns are chosen as a function of the expansion rate and the strength in the expanded state desired for the sheath.
Furthermore, the application filed under number PCT/FR2013/051381 describes a hybrid elastic yarn provided to be used as peripheral yarn for the manufacture of the tubular sheath of FR 2,910,047.
The tubular sheath of FR 2,910,047 and the elastic yarn of PCT/P2013/051381 correspond perfectly to the main industrial objective for which they are intended, i.e., the prevention of the explosion of inflatable sleeves, owing to control of the profile of the tubular sheath in the expanded state. They make it possible to obtain, in the expanded state, a spindle-shaped tubular sheath profile, shown in FIG. 1. The sheath 1, in FIG. 1, has, in the expanded state, a cylindrical central segment 3 and first and second longitudinal ends 5 and 7 that are substantially frustoconical. The ends 5 and 7 have a straight section that decreases from the central segment to a ring 9 fixing the sheath 1 to the mandrel 11. The opening angle of the frustoconical ends is small, for example smaller than 30°.
In such a sheath, the longitudinal yarns only undergo very slight elongation when the sheath goes from its idle state to its expanded state. The spindle shape is controlled by gradually varying the minimum elongation level of the peripheral yarns. The maximum elongation level gradually increases along the ends 5 and 7 up to the central segment 3.
However, a tubular sheath of this type cannot be used in the case where the desired profile at the longitudinal ends of the sheath, in the expanded state, has a hemispherical shape. Such a profile is shown in FIG. 2. Indeed, for such a hemispherical profile, the diameter of the tubular sheath in the expanded state varies quite quickly at the ends. In order to obtain such a result, the maximum ultimate strength of the peripheral yarns should thus vary quite quickly from one turn to the next, which is difficult to achieve.